The present invention relates to a method and apparatus for supplying fuel to and cooling the high power or takeoff fuel injector of a gas turbine engine having a dual head combustion chamber.
Modern turbojet engines comprise dual head combustion chambers fed with fuel from a double injector comprising a first fuel supply for a low power fuel injector and a second fuel supply for the high power or takeoff fuel injector. The low power fuel injector of the dual head combustion chamber is permanently supplied with fuel regardless of the operational mode of the turbojet engine. On the other hand, the high power or takeoff fuel injector is supplied with fuel only beyond a minimum operating mode corresponding to approximately 20% of the maximum operational mode of the engine. Accordingly, when the engine is operating in a low power mode, the high power or takeoff fuel injector must be cooled to preclude coking of the fuel in its fuel feed circuit.
It is known to fit a high power or takeoff fuel injector with a cooling system wherein the fuel feeding the low power fuel injector is made to circulate through the high power fuel injector. However, the known systems are complex insofar at they entail two fuel supplies and three fuel circulating tubes, a first tube wherein the fuel to the low power injector circulates centripetally and extending as far as the end of the high power fuel injector, a second tube coaxial with the first tube and connecting the high power fuel injector end to the low power fuel injector, the fuel feeding the low power injector circulating centrifugally in the second tube, and a third tube midway between the first and second tubes wherein the fuel feeding the high power fuel injector circulates centripetally. In such systems, external complimentary means must be provided to distribute the fuel between the two circuits depending upon the operation mode of the turbojet engine.
French Patent No. 2,441,725 discloses a dual head combustion chamber having a single fuel feed wherein each bypass conduit is directly connected to the low power fuel injector nozzle such that part of the fuel is bypassed towards the high power fuel injector nozzle by a check valve controlled by a regulator in the injector head which is, in turn, controlled by an external drive means. In this system, the relatively cool fuel cools the valve rod in the immediately adjacent vicinity, but does not permit the cooling of the high power fuel injector all the way to its distal end.